Rising damp & crumbling plinth advice please!

[Dixonm5]

Hi there everyone - I've just taken ownership of a 1920's mid-terrace, and as part of the survey the crumbling plinth and some rising damp was noted. Upon getting a very recommended damp/timber preservation company round to map the house for issues, among many other things, damp across a lot of the front of the house was noted. This is combined with a rotting joist in one corner, as I had already lifted the floor in this area using existing cuts in the floorboards (most likely for gas fire installation). Their suggestion was to clear out the aerial cables that had been routed between the garden wall and the house (see pics), clear any debris from that gap, and they also pointed out that the whole house had been repointed with cement on top of the original lime. The damp joist though they thought was caused by a failure in the slate DPC at some point, and so along with adding a vertical DPC to stop anything going into the party wall from the front, they're also going to inject a new DPC when they replace the joist to make sure it's continuous.

Since that survey, the plinth has crumbled even more and now I'm just confused. The damp company told me to get the shingles away from the plinth, which I've done, but it's revealed a concrete "border" all the way around the front. I've tried looking for the original slate DPC, but even where the plinth has come away I can't see it (although some higher layers of brick are obscured by the cement mortar). I was hoping to install a french drain at the front to keep as much stationary water away from the plinth as possible, but now I'm confused as to whether the plinth itself is the problem. It appears original, as it's got cast iron airbricks and is identical to the plinth and airbrick setup next door, which is in "more original" condition than my own property. Behind it is also yellow bricks like at the back of the property, rather than the red of the rest of the frontage. One slight difference is that over the years mine has been painted black many times, whereas next doors is "naked". The plinth and concrete border are both pre-1960, as the house was my fathers growing up and he remembers both features from when he was young.

Could it be the culprit for bridging the DPC, or is it potentially something else? And how can I prevent doing all this work inside on the joists and DPC to end up fixing nothing by still having something causing an issue? How do I fix the plinth, if it's keep-able?

I've taken as many photos as I could (thumbnails in post, full-size as attachments), so hopefully one will provide some insight - but I've never done anything like this before, so I really don't know where to start, I hope my many questions are okay!

 

[MatthewC]

Hi there, and welcome. You have asked lots of questions so to start with, here are some quick answers as a starter for ten:

1. The cement pointing over the lime mortar certainly will not help.
2. Do you know for sure that there is a slate DPC?
3. The proposal to inject a DPC quite possibly will not help either. People who recommend those often are simply trying to sell their stuff, rather than actually fix the root cause.
4. What is it like under the floor inside? How much space, and is it ventilated? (I found a cast vent had been blocked inside to prevent it doing exactly what it was meant to!) I would add another vent on the floor on the far side in order to improve the underfloor ventilation.
5. From the photo, that brickwork under the window looks a bit newer than 1920, so I wonder if some rebuilding has already been done?
6. What is the difference in height between the ground outside and the floor inside? You need to get the ground lower than the floor by several inches.
7. What is the roof above the bay window like? Has there been water pouring off the roof?
8. The water must have come from somewhere, and the cement and the black (bituminous?) paint will not have helped it escape.

HTH

MatthewC

 

[Dixonm5]

Hi there, and welcome. You have asked lots of questions so to start with, here are some quick answers as a starter for ten:

1. The cement pointing over the lime mortar certainly will not help.
2. Do you know for sure that there is a slate DPC?
3. The proposal to inject a DPC quite possibly will not help either. People who recommend those often are simply trying to sell their stuff, rather than actually fix the root cause.
4. What is it like under the floor inside? How much space, and is it ventilated? (I found a cast vent had been blocked inside to prevent it doing exactly what it was meant to!) I would add another vent on the floor on the far side in order to improve the underfloor ventilation.
5. From the photo, that brickwork under the window looks a bit newer than 1920, so I wonder if some rebuilding has already been done?
6. What is the difference in height between the ground outside and the floor inside? You need to get the ground lower than the floor by several inches.
7. What is the roof above the bay window like? Has there been water pouring off the roof?
8. The water must have come from somewhere, and the cement and the black (bituminous?) paint will not have helped it escape.

HTH

MatthewC

Hi Matthew!

Thanks for the response!

2. Our surveyor was relatively confident, knowing when the house was built and the area it's in - we've got very wet and clay-y soil, so he said that whilst he can't see an exposed DPC, it would be shocking given the lack of severe damp if there wasn't one. Hence his "informed guess" that it was either hidden by repointing, or under the plinth. Or maybe I just can't see it...

3. I've read this a lot - my weighing up of the suggestion was that if we have a slate DPC, it can't make it any worse, and if we don't, it can help mitigate any issues. Obviously on the understanding that I need to get all the water sources sorted too... They're a very very locally reputable company, and are also doing the joist and plasterwork - for a fairly reasonable sum

4. There's not the worlds greatest amount of space - it's difficult to judge, but I would guess at 4 bricks worth. Not a crawl space, but not touching the floor either. It's got 3 air-bricks, on the bay window, and all appear clear. The rear of the house has been extended, but there are airbricks there too so our surveyor thinks that the rear is still being ventilated - the floor in the extension is block and beam.

5. I'm not sure which section you mean, but there would have been nothing recent - we have the total property history from the 1960s onwards, and the white decorative surround on the bay is still in (need of restoration....) original condition. Potentially my phone has done something with the colours, although the bricks used are far more orange than I see online with terraces of this age, as is next door (built at the same time). The garden wall is 2008, for comparison sake. What indicated that? Maybe it's something for me to look into if it was done pre-1960 but post-build?

6. It's really difficult to tell, but just going on what's in my head, I'd say that the floor is level with the top of the bricks above the plinth. I can double check tomorrow though. The path is midway up the plinth, then there's a layer of airbricks under the door tread, then the door tread sits about on top of the floor itself.

7. The roof is (now) fine, although in the corner where the garden wall (and brown fibre box) is, we had to have a total gutter blockage removed which apparently caused the guttering to appear as though it was leaking. This was highlighted, so may be an additional cause of water.

8. I agree - next doors plinth isn't painted - I'm at a bit of a loss what to do with the plinth. We love the look, and it appears at least to be original (and not a 70's damp-proofing job) - but assuming that the original builders did everything perfect is foolish, especially as knowledge of building materials and their effects advances....

 

[Dixonm5]

Hi there, and welcome. You have asked lots of questions so to start with, here are some quick answers as a starter for ten:

1. The cement pointing over the lime mortar certainly will not help.
2. Do you know for sure that there is a slate DPC?
3. The proposal to inject a DPC quite possibly will not help either. People who recommend those often are simply trying to sell their stuff, rather than actually fix the root cause.
4. What is it like under the floor inside? How much space, and is it ventilated? (I found a cast vent had been blocked inside to prevent it doing exactly what it was meant to!) I would add another vent on the floor on the far side in order to improve the underfloor ventilation.
5. From the photo, that brickwork under the window looks a bit newer than 1920, so I wonder if some rebuilding has already been done?
6. What is the difference in height between the ground outside and the floor inside? You need to get the ground lower than the floor by several inches.
7. What is the roof above the bay window like? Has there been water pouring off the roof?
8. The water must have come from somewhere, and the cement and the black (bituminous?) paint will not have helped it escape.

HTH

MatthewC

Just as a follow up, I've gotten some pictures of beneath the floor - I believe it shows the DPC - and I'd need my laser to confirm from the outside, but I believe I can see the airbrick and it's on the brick layer above the DPC. It also shows floor-height versus ground level.

 

[Cubist]

Just a quick addition to the comments and thoughts already shared. It was not uncommon for builders to use higher quality/ different coloured/ more expensive bricks on the frontages of some houses to enhance kerb appeal. Frequently they would however use lower quality bricks in the lower courses as part of any footings/foundations and below any DPC. There was also a trend among some owners to hide these lower courses, if exposed, with a cement capping that would often be painted. Aside from the aesthetics the cement capping also helped to limit rain penetration into the inferior bricks and thus reduce spalling. It may be well to consider whether removal of the capping is a wise move.

 

[Dixonm5]

With the lack of drainage in front of the property (concrete border), and the location of the DPC - what effect would that capping have, and what material should it be redone with?

 

[Cubist]

With the lack of drainage in front of the property (concrete border), and the location of the DPC - what effect would that capping have, and what material should it be redone with?

I would propose a lime based concret. But whatever is used the DPC must not be bridged.

 

[Dixonm5]

So if the DPC is below current "concrete" level, and I can't bridge it, do I:

1) Remove concrete slab and excavate dirt to 1 brick below DPC

2) Backfill to DPC level with gravel

3) Begin lime cement capping at DPC level ("floating" slightly over the gravel and take it to previous height.

So un-capped brickwork below DPC and the DPC itself is exposed via gravel, yellow bricks above DPC line/gravel are covered with lime cement capping, and rest of house is as it was?

 

[Cubist]

That would work I think. You just need to make sure the DPC is clear and care is taken not to damage to the integrity of the foundation or under-cut it.

 

[Smith Heritage]

Certainly some good advice already given here so I don’t want to repeat what has been said. But I will reiterate that any chemicals or injected DPCs are not the right course of action. Find the cause and deal with it, chemicals only try and hide it.

If you get stuck, get a damp and timber survey from an independent RICS surveyor